1. Field of the Invention
The present invention relates to a sputtering apparatus for depositing (or forming) a film by generating stable magnetron discharging in a high vacuum. It also relates to a sputtering film deposition apparatus which is suitable for manufacturing an element of a magneto-resistance head which replays the magnetic records by utilizing a magnetoresistance effect. It still furthermore relates to a method of manufacturing an element for a magnetoresistance head.
2. Description of the Related Art
As a sputtering apparatus, there is conventionally known the following type of apparatus. Namely, a permanent magnet is disposed behind a target. A magnetic field is generated in front of the target by this permanent magnet. A cathode electric potential is charged to the target to thereby generate magnetron discharge in front of the target. Sputtered particles from the target are thus caused to adhere or deposit in the form of a thin film to a substrate which is disposed opposite to the target. In this kind of magnetron sputtering apparatus with the above-described structure, however, there is a disadvantage in that the discharge does not occur or will become unstable in the vacuum in the order of 10.sup.-2 Pa, with the result that the film deposition can no longer be performed. In order to eliminate this kind of disadvantage, there has been proposed a magnetron sputtering apparatus of a type in which an radiofrequency (RF) induction coil is disposed in front of a target to thereby overlap (or combine) the electric discharge generated by electric charging to the RF induction discharge coil and the magnetron discharge together. This type of apparatus is called an inductively coupled RF plasma-assisted magnetron sputtering apparatus. In this apparatus, both direct current and high frequency can be used as the sputtering electric power. With this type of magnetron cathode in which a magnet is disposed behind the target, the uniformity in the thickness distribution of the film to be deposited on the substrate is poor. For example, in order to attain a uniformity of 3% or less within a surface of a substrate of 6 inches in diameter, a cathode of 12 inches must be provided. It has therefore a disadvantage in that the film deposition apparatus becomes very large in size in case a large number of cathodes must be provided in order to deposit multiple layers of films on the substrate.
Recently, a magnetoresistance head is under development as a means for replaying or reproducing magnetic records that have been recorded in high density. The above-described magnetoresistance head is to obtain a magnetoresistance effect by sequentially laminating (or repeating) a ferromagnetic film and a non-magnetic film. It has advantages in that the replay output does not depend on the peripheral speed of a recording disk, that there is no limit to the resonance frequency by the coil, and that the impedance noises can be reduced. For the above-described reasons, the magnetoresistance head is suitable as the means for replaying the high-density magnetic records. There are various kinds and structures of magnetoresistance heads. For example, as a shield type of magnetoresistance head, there is known one which has the film structure as shown in FIG. 1. In the figure, reference letter "a" denotes a substrate which is high in wear-resistance and low in thermal expansion such as AlTiC or the like. Reference letter b denotes a lower shield layer of FeSiAl or the like. Reference letter c denotes a lower gap layer of Al.sub.2 O.sub.3 or the like. Reference letter d denotes a ferromagnetic hard bias layer of a cobalt (Co) based alloy, Fe.sub.3 O.sub.4 or the like. Reference letter e denotes a ferromagnetic soft adjacent layer (SAL) of an NiFe based alloy, cobalt (Co) based amorphous or the like. Reference letter f denotes a magnetic separation layer of tantalum (Ta), copper (Cu) or the like. Reference letter g denotes a magnetoresistance (MR) stripe (ferromagnetic thin film) of NiFe or the like. Reference letter h denotes an electrode of Cu, gold (Au), tungsten (W) or the like. Reference letter i denotes an upper gap layer of Al.sub.2 O.sub.3 or the like. Reference letter j denotes an upper shield layer of NiFe or the like. The MR stripe layer g functions to convert the signal magnetic field in the record medium to voltage through magnetoresistance effect. The magnetic separation layer f functions to magnetically separate the MR stripe layer g and the SAL layer e. The SAL layer e operates to apply a lateral bias to the MR stripe layer g. The hard bias layer d operates to magnetize the SAL layer e.
It is preferable to magnetically record on the record medium at an ultrahigh density. In order to well replay the magnetic record of ultrahigh density, e.g., of 1-20 Gbit/in.sup.2 or more which is recorded on the record medium, the following proposal has been made. Namely, the ferromagnetic thin film which constitutes the MR stripe layer g is constructed in a single magnetic domain in which there is only one magnetic domain. On top of this, two or three layers of a nonmagnetic separation layer such as of Cu or the like, a magnetic layer of Co, and an antiferromagnetic layer of FeMn or the like are laminated in two or three layers to thereby form a spin valve magnetoresistance film. Or else, on top of the MR stripe layer g of single magnetic domain structure, there are alternately laminated, e.g., eight times, a layer made up of a set of a magnetic separation layer of Cu, a magnetic layer of Fe, and an anti-ferromagnetic layer of Ni or the like, thereby depositing a magnetic multilayer film such as a giant magnetic resistance film.
In depositing this kind of multilayer films, an ion beam sputtering apparatus is used, but it is poor in productivity. On the other hand, the applicant of the present invention has developed an inductively coupled RF plasma-assisted magnetron sputtering apparatus (called a helicon sputtering apparatus) in which, as shown in FIG. 2, an RF induction discharge coil 1 is disposed above a planer magnetron cathode k and in which sputtering can be performed in an ultrahigh vacuum. It has been found that a multiple layer film of a magnetoresistance head can be formed also by using this apparatus.
The above-described inductively coupled RF plasma-assisted magnetron sputtering apparatus has an advantage in that the film deposition by sputtering can be made while the inside of the film deposition chamber is maintained in a clean atmosphere of a high vacuum. However, the target is a consumable and must be replaced. When the sputtering apparatus is removed out of position to replace the worn target, the clean atmosphere inside the film deposition (or film-forming) chamber is destroyed. In case an ultrahigh vacuum in the order of 10.sup.-7 Pa or more (the term "more" means a vacuum of a larger degree, i.e., a vacuum towards 10.sup.-8 Pa) is required as the vacuum pressure inside the film deposition chamber, it is necessary to bake the inside of the film deposition chamber, in order to obtain a clean atmosphere at a short evacuating time, before reusing it after the sputtering apparatus has been mounted. In this sputtering apparatus, however, the target that is bonded to a backing plate will be removed out of position or the RF coil is damaged due to the heat of baking. This kind of damages are not favorable and must be avoided.
In order to manufacture a magnetoresistance head of multiple magnetic layers as described above, it is necessary to deposit magnetic films and magnetic separation layers which are clean in the film surfaces and are extremely as thin as in the order of 0.4-11 nanometers (nm) in multiple layers. For example, when an iron (Fe) film is formed on a silicon substrate to a thickness of 5.0 nm and, on top of it, a magnetic separation layer of Cu of a certain thickness and a layer of NiFe of 1 nm thick are alternately laminated for 20 times to thereby form a magnetic multiple film (giant magnetoresistance film), the magnetoresistance value (Magnetoresistance ratio, MR ratio) of this film will largely vary with the change in the thickness of the magnetic separation layer of Cu in the order of about 10 Angstroms, as shown in FIG. 3. It is therefore not easy to deposit the magnetic separation layer to a uniform thickness of 1 nm. Although the MR value at the second peak in the neighborhood of 2.1 nm in FIG. 3 is low, this thickness is considered to be suitable for practical use because the sensitivity to the change in the magnetic field is good. In order to efficiently form a 2.1 nm thick Cu film or an about 10 nm thick magnetic film which are flat and clean in the surfaces, an accurate film thickness control below 0.1 nm and an extremely clean atmosphere become necessary. The conventional ion beam sputtering apparatus is poor in productivity. The conventional type of magnetron sputtering apparatus, on the other hand, has a high atmosphere pressure and is too high in film deposition rate and is, therefore, difficult to manufacture it. Further, a mass-production system for manufacturing this kind of multiple layer film by using the inductively coupled RF plasma-assisted magnetron sputtering apparatus (helicon sputtering apparatus) has not been developed in concrete yet. In addition, as described above, in the conventional type of sputtering apparatus, the uniformity in the film thickness is poor, and there is the necessity of using a large-scale cathode which is far larger than the substrate. As a result, the film deposition chamber becomes large in size, and a multi-chamber type of film deposition apparatus in which multiple-layer films are deposited by providing a plurality of film deposition chambers becomes very large in size. Therefore, it has not been employed in practical manufacturing line.
Further, the magnetoresistance head is manufactured in a large number of pieces by depositing the necessary magnetic layers on substrates of about 5 inches in diameter and then by cutting the substrates into predetermined dimensions. However, if the direction of magnetization of the magnetic layers is not substantially uniform in each of the substrates, the electric resistance values of the MR stripe layers may vary from substrate to substrate and, consequently, homogeneous magnetoresistance heads cannot be obtained.